The present invention relates to volume adjustable manual pipettes and, more particularly, to a manually-operated pipette equipped with an electronic piston position sensor and user interface.
U.S. Pat. No. 3,827,305 (“the '305 patent”) describes one of the earliest commercially available digitally adjustable air displacement pipettes. To provide for volume adjustment, the pipette includes a threaded shaft extending through a fixed nut. Manual turning of the shaft produces axial movement of a stop member for limiting axial movement of a plunger to define a volume setting for the pipette. The volume setting is displayed on a mechanical micrometer display comprising a series of indicator rings each encircling the threaded shaft.
U.S. Pat. No. 4,909,991 describes a later commercially available single channel manual pipette manufactured by Nichiryo Co. Ltd., Tokyo, Japan. The Nichiryo pipette includes an elongated hand-holdable housing for an upwardly spring biased plunger. An upper end of the plunger extends above a top of the housing and carries a control knob for thumb and finger engagement in manually turning the plunger and for axially moving the plunger in the pipette housing between an upper stop and a lower stop at which all liquid within a tip secured to a lower end of the housing is expelled by the downward movement of the plunger. The upper stop is axially adjustable within the housing in response to a turning of a hollow volume adjustment screw or shaft keyed to the plunger. The axial adjustment of the upper stop adjusts the volume of liquid that the pipette is capable of drawing into the tip in response to upward movement of the plunger to the upper stop. The pipette also includes a lock mechanism including a lock knob for locking the plunger against rotation to thereby set the upper stop in a fixed position and hence set the volume adjustment for the pipette.
In pipettes such as these, the volume setting is typically read from a stacked series of indicator rings, each bearing the digits from zero to nine. The least significant (usually bottom-most) ring is coupled to the position of the volume adjustment screw, and is calibrated such that a single-unit change in the pipette volume (as defined by the position of the upper stop) will be reflected by a single-unit change in the digit shown on the coupled ring. The remaining rings serve as counters of tens, hundreds, or thousands of the increment shown in the least significant ring.
Now, more than thirty years after volume indicator of the ''305 patent made its initial appearance, the most common manual pipettes still use mechanical volume indicators very similar in operation to the one disclosed therein. It will be appreciated, however, that mechanical volume indicators such as these have several shortcomings. A mechanically coupled indicator will have some degree of slack, or backlash, resulting from the linkage between the screw that sets the upper stop and the displayed digits. If a user turns the screw in one direction to reach a desired setting but overshoots, it may be difficult for small adjustments in the opposite direction to be registered in the volume indication because of this effect. Moreover, with strictly mechanical arrangements such as the one disclosed in the '305 patent, it is difficult to accurately compensate for any nonlinearities present in the volume settings, for example at very small volumes compared to the total capacity of the pipette, even when those nonlinearities are known in advance and consistent across a manufactured lot of pipettes. And when non-linearities are inconsistent and arise from manufacturing variances, it is nearly impossible to compensate fully with a mechanical apparatus.
U.S. Pat. No. 6,601,433 describes the commercially available “Ovation” pipettes sold by Vistalab Technologies, Inc. In these pipettes, and as described in the patent, the volume adjusting upper stop is positioned by an electric motor drive mechanism with a digital control. The digital control enables calibration of volume settings, but because there is no electronic sensing of the manually operated plunger position, the precise position of the plunger cannot be ascertained at any given time, and accordingly, accurate calibration of the volume adjusting upper stop might not always be reflected in the results of using the pipette. Moreover, the motor drive apparatus imparts unnecessary complexity to the device and requires a significant amount of power to operate, and consequently, reasonably capacious batteries are also needed. Both the motor drive and the batteries add size, weight, and considerable expense to the pipette.
PCT Publication No. WO 2005/093787 A1 describes the “Ultra” Pipette available from Gilson, SAS, of Villiers le Bel, France. The Gilson Ultra pipette uses conductive tracks and corresponding contact brushes to send sequences of pulses to a microprocessor when the volume adjustment screw is turned. In this manner, by counting pulses, the microprocessor can identify when the adjustment screw is moved either up or down, and based on prior position information a new position can be calculated. But as a result of this design, the microprocessor cannot determine the absolute position of the stop with no prior data. If power is removed or a malfunction occurs, the volume reading must be recalibrated by moving the adjustment screw to a known position and resetting the pipette, and as with traditional pipette adjustment mechanisms, it can take many turns of the screw to accomplish this. Moreover, the brush-on-track encoder design is susceptible to wear and unreliability over the course of time, and because the encoder is mechanically linked to the adjustment mechanism, slack and backlash can occur.
Other volume adjustable manual pipettes with electronic digital displays have been developed and are disclosed in U.S. Pat. Nos. 4,567,780; 4,763,535; and 5,892,161.
For a more complete understanding of the current state of the art relative to the volume adjustability of manual pipettes, each of the above-identified patents is incorporated by reference into this application.
U.S. Pat. No. 6,428,750 issued Aug. 6, 2002 to the assignee of the present invention, and U.S. Pat. No. 7,175,813 issued Feb. 13, 2007 also to the assignee of the present invention, describe an improved volume adjustable manual pipette having a quick set volume adjustment mechanism and a plunger position sensor. The volume setting of the pipette is monitored by the sensing and control circuitry to provide a real time display of the volume setting of the pipette on the electronic digital display. While the quick set and volume display features represent a considerable advance in the art of manual pipettes, the described pipette does not contemplate enhanced pipetting functionality beyond the ability to quickly change volume settings, or improved calibration techniques reducing the likelihood of mechanical slack or unreliability to affect the utility of the pipette.
There is a continuing need for a volume adjustable manually operated pipette including an accurate and highly visible display of pipetting volume. A pipette capable of measuring the position of a manually driven plunger unit, calibrating that measurement, and displaying the position in real-time meets this need, and the real-time measurement, calibration, and display would enable enhanced functionality over traditional manually operated pipettes.